1. Field of the Invention
This invention relates to fluoroalkoxysulfur fluorides, their preparation and use as fluorinating agents to replace hydroxyl groups with fluorine in organic molecules. Also of concern are solutions of the intermediate lithium fluoroalkoxides in halocarbon solvents.
2. State of the Art
Baum, in J. Am. Chem. Soc., 91, 4594 (1969), describes the preparation of 2-fluoro-2,2-dinitroethoxysulfur trifluoride by reaction of 2-fluoro-2,2-dinitroethanol with sulfur tetrafluoride. This compound would not have utility as a fluorinating agent because its two nitro groups would make it explosive. Furthermore, isolation of fluorinated reaction products from a reaction mixture containing this compound would be complicated by its low volatility and that of its expected by-products.
Darragh et al, in J. Chem. Soc., Dalton Trans., 1975, 218, describe the preparation of several aryloxysulfur trifluorides and diaryloxysulfur difluorides by the reaction of aryl silyl ethers and sulfur tetrafluoride. These compounds would not have fluorinating utility because they are generally unstable. In addition, the isolation of fluorinated reaction products, if formed, from reaction mixtures containing the aryloxysulfur trifluorides, would be complicated by the low volatility of the aryloxysulfur trifluorides and their expected by-products. The authors state that they made unsuccessful attempts to prepare alkoxy derivatives of sulfur (IV) fluorides.
Among the most useful known fluorinating agents are the dialkylaminosulfur trifluorides (DAST) of U.S. Pat. No. 3,914,265 and the bis(dialkylamino)sulfur difluorides of U.S. Pat. No. 3,888,924. The fluoroalkoxysulfur fluorides of this invention offer certain advantages over these known fluorinating agents because they are safer to use at elevated temperatures, they are more soluble in non-polar solvents, and aqueous work-up can be avoided because the by-products are volatile.